Retro-reflective thread, method of manufacturing same and a textile

ABSTRACT

Disclosed is a retro-reflective thread  100  including an internal section  10 ; a plurality of fibers  12 , each fiber comprising a respective longitudinal axis and a respective surface and each fiber comprising a first material that is at least partially optically transmissive, and wherein said plurality of fibers are configured with their respective longitudinal axes substantially co-linearly aligned with one another and said plurality of fibers are interconnected in series around said internal section and wherein a first part  12   b  of said respective surface of each of said plurality of fibers faces into said internal section; and a reflective material  14  provided on said first part of said respective surface of each of said plurality of fibers.

This application is a division of application Ser. No. 15/051,966, filedFeb. 24, 2016, now U.S. Pat. No. 10,427,367.

FIELD OF THE INVENTION

The present invention relates to a retro-reflective thread and to atextile comprising at least one said retro-reflective thread. Thepresent invention further relates to a method of manufacturing aretro-reflective thread.

BACKGROUND

Retro-reflectivity is the property where incident light from a localizedsource, for example a headlight, flashlight, or the moon, is mostlyreturned to the source even if the reflecting surface is not facing thesource. In addition, such surfaces scatter little light in otherdirections. Retro-reflective surfaces increase visibility in lowvisibility conditions. Clothes, decalcomanias, and signs are major endproducts for retro-reflective surfaces. Typically, such surfaces areconstructed from an array of miniaturized refractive elements bondedonto a reflective surface. Common retro-reflectors include metal-coatedhigh index glass spheres and cube corner prisms with metalized backcoatings. The retro-reflective surfaces themselves are sown or otherwisebonded onto an article that is desired to have an area ofretro-reflectivity. Fibers with innate retro-reflectivity have remainedelusive to date. Prior attempts to produce, via extrusion, such a fiberhave included uniform circular cross-section fibers and star-shapedcross-section fibers, the latter being designed to mimic a cube cornerretro-reflector with 90° inner angles and a reflective coating.

Although known retro-reflectors and techniques for using them haveproven useful, there are disadvantages and drawbacks. Room forimprovement remains and would be a welcome advance in the art.

SUMMARY OF THE INVENTION

In one aspect, the invention provides a retro-reflective threadcomprising an internal section, a plurality of fibers and a reflectivematerial. Each said fiber comprises a respective longitudinal axis and arespective surface. Each said fiber comprises a first material that isat least partially optically transmissive. Said plurality of fibers areconfigured with their respective longitudinal axes substantiallyco-linearly aligned with one another. Said plurality of fibers areinterconnected in series around said internal section and a first partof said respective surface of each of said plurality of fibers facesinto said internal section. Said reflective material is provided on saidfirst part of said respective surface of each of said plurality offibers.

In an embodiment, each of said plurality of fibers is substantiallycircular in cross-section. In an alternative embodiment, each of saidplurality of fibers is substantially elliptical in cross-section.

In an embodiment, said internal section is substantially circular incross section and has radius, R_(core), and each said fiber has aradius, R_(surface). Said plurality of fibers, N, is inverselyproportional to the ratio of R_(surface) to R_(core).

In an embodiment, interconnected in series comprises said plurality offibers arranged in a spaced series and the retro-reflective threadfurther comprises a plurality of connecting elements. Each of saidplurality of connecting elements being located between and interconnectsa respective pair of said plurality of fibers.

In an alternative embodiment, interconnected in series comprises each ofsaid plurality of fibers arranged touching a directly preceding one ofsaid plurality of fibers and touching a directly subsequent one of saidplurality of fibers.

In an embodiment, each of said plurality of fibers arranged justtouching a directly preceding one of said plurality of fibers and justtouching a directly subsequent one of said plurality of fibers, and saidplurality of fibers, N, is given by

$N = \frac{\pi}{\arcsin( \frac{R_{surface}}{R_{core}} )}$

In an embodiment, the maximum radius, R_(surface), of each of saidplurality of fibers is given by,

${R_{surface} = {R_{core}{\sin( \frac{\pi}{N} )}}},$where N is said plurality of fibers.

In an embodiment, said first material is a substantially transparentpolymer. In an embodiment, said first material is one of polypropyleneand polyester. In an alternative embodiment, said first material is aglass.

In an embodiment, said first material has a refractive index in therange 1.5 to 2.2. In an embodiment, said first material has a refractiveindex in the range 1.85 to 2.05. Preferably, said first material has arefractive index of substantially 1.9.

In an embodiment, said first material is substantially opticallytransmissive at visible wavelengths of light. In an alternativeembodiment, said first material is substantially optically transmissiveat infra-red wavelengths of light and said first material issubstantially absorptive at visible wavelengths of light.

In an embodiment, said reflective material is one of a reflective metal,a reflective alloy and a polymer doped with reflective particles.

In an embodiment, said reflective material comprises a coating providedon said first part of said respective surface of each of said pluralityof fibers.

In an embodiment, said internal section comprises a polymer core. In analternative embodiment, said internal section comprises a core of saidreflective material.

In an embodiment, said internal section has one of a circularcross-section and a non-circular cross-section.

In another aspect, the invention provides a textile comprising at leastone retro-reflective thread. The retro-reflective thread comprises aninternal section, a plurality of fibers and a reflective material. Eachsaid fiber comprises a respective longitudinal axis and a respectivesurface. Each said fiber comprises a first material that is at leastpartially optically transmissive. Said plurality of fibers areconfigured with their respective longitudinal axes substantiallyco-linearly aligned with one another. Said plurality of fibers areinterconnected in series around said internal section and a first partof said respective surface of each of said plurality of fibers facesinto said internal section. Said reflective material is provided on saidfirst part of said respective surface of each of said plurality offibers.

In an embodiment, each of said plurality of fibers is substantiallycircular in cross-section. In an alternative embodiment, each of saidplurality of fibers is substantially elliptical in cross-section.

In an embodiment, said internal section is substantially circular incross section and has radius, R_(core), and each said fiber has aradius, R_(surface). Said plurality of fibers, N, is inverselyproportional to the ratio of R_(surface) to R_(core).

In an embodiment, interconnected in series comprises said plurality offibers arranged in a spaced series and the retro-reflective threadfurther comprises a plurality of connecting elements. Each of saidplurality of connecting elements being located between and interconnectsa respective pair of said plurality of fibers.

In an alternative embodiment, interconnected in series comprises each ofsaid plurality of fibers arranged touching a directly preceding one ofsaid plurality of fibers and touching a directly subsequent one of saidplurality of fibers.

In an embodiment, each of said plurality of fibers arranged justtouching a directly preceding one of said plurality of fibers and justtouching a directly subsequent one of said plurality of fibers, and saidplurality of fibers, N, is given by

$N = \frac{\pi}{\arcsin( \frac{R_{surface}}{R_{core}} )}$

In an embodiment, the maximum radius, R_(surface), of each of saidplurality of fibers is given by,

${R_{surface} = {R_{core}{\sin( \frac{\pi}{N} )}}},$where N is said plurality of fibers.

In an embodiment, said first material is a substantially transparentpolymer. In an embodiment, said first material is one of polypropyleneand polyester. In an alternative embodiment, said first material is aglass.

In an embodiment, said first material has a refractive index in therange 1.5 to 2.2. In an embodiment, said first material has a refractiveindex in the range 1.85 to 2.05. Preferably, said first material has arefractive index of substantially 1.9.

In an embodiment, said first material is substantially opticallytransmissive at visible wavelengths of light. In an alternativeembodiment, said first material is substantially optically transmissiveat infra-red wavelengths of light and said first material issubstantially absorptive at visible wavelengths of light.

In an embodiment, said reflective material is one of a reflective metal,a reflective alloy and a polymer doped with reflective particles.

In an embodiment, said reflective material comprises a coating providedon said first part of said respective surface of each of said pluralityof fibers.

In an embodiment, said internal section comprises a polymer core. In analternative embodiment, said internal section comprises a core of saidreflective material.

In an embodiment, said internal section has one of a circularcross-section and a non-circular cross-section.

In a further aspect, the invention provides a method of manufacturing aretro-reflective thread. The method comprises steps a. to c. Step a.comprises forming a thread by: forming a core comprising a firstsurface; and forming a plurality of fibers. Each said fiber comprises arespective longitudinal axis and a respective surface. Said plurality offibers are configured with their respective longitudinal axessubstantially co-linearly aligned with one another and said plurality offibers are interconnected in series around said core. Each said fibercomprises a first material that is at least partially opticallytransmissive. Step b. comprises removing said core to form a void. Saidcore is removed such that a first part of said surface of each of saidplurality of fibers faces into said void. Step c. comprises delivering areflective material in a fluid state into said void, thereby providingsaid reflective material on said first part of said surface of each ofsaid plurality of fibers.

In an embodiment, forming said plurality of fibers comprises formingsaid plurality of fibers in a spaced series and forming a plurality ofconnecting elements, each connecting element being formed between andinterconnecting a respective pair of said plurality of fibers.

In an alternative embodiment, forming said plurality of fibers comprisesforming each of said plurality of fibers to be touching a directlypreceding one of said plurality of fibers and to be touching a directlysubsequent one of said plurality of fibers.

In an embodiment, said core comprises a second material that is solublein a first solvent and said first material is insoluble in said firstsolvent. In step b., removing said core comprises dissolving said corein said first solvent. In an embodiment, said second material is a watersoluble polymer and said first material is a non-water soluble polymer.In step b., removing said core comprises dissolving said core in water.

In an embodiment, said first material is one of polypropylene andpolyester.

In an embodiment, in step c. providing said reflective material on saidfirst part of said surface of each of said plurality of fiberscomprises: coating said first part of said surface of each of saidplurality of fibers with said reflective material in said fluid state;removing an amount of said reflective material not coating said firstpart of said surface of each of said plurality of fibers; and enablingsaid reflective material coating said first part of said surface of eachof said plurality of fibers to solidify.

In an alternative embodiment, in step c. providing said reflectivematerial on said first part of said surface of each of said plurality offibers comprises substantially filling said void with said reflectivematerial in said fluid state and enabling said reflective material tosolidify.

In an embodiment, the method further comprises step e. comprisingsubstantially filling said void with a polymer in a fluid state andenabling said polymer in said fluid state to solidify.

In an embodiment, forming said core and forming said plurality of fiberscomprises simultaneously extruding said core and said plurality offibers.

In an embodiment, said reflective material is one of a reflective metal,a reflective alloy and a polymer doped with reflective particles.

In an embodiment, in step a. each of said plurality of fibers is formedhaving a substantially circular cross-section. In an alternativeembodiment, in step a. each of said plurality of fibers is formed havinga substantially elliptical cross-section.

In an embodiment, said internal section is substantially circular incross section and has radius, R_(core), and each said fiber has aradius, R_(surface). Said plurality of fibers, N, is inverselyproportional to the ratio of R_(surface) to R_(core).

In an embodiment, each of said plurality of fibers arranged justtouching a directly preceding one of said plurality of fibers and justtouching a directly subsequent one of said plurality of fibers, and saidplurality of fibers, N, is given by

$N = \frac{\pi}{\arcsin( \frac{R_{surface}}{R_{core}} )}$

In an embodiment, the maximum radius, R_(surface), of each of saidplurality of fibers is given by,

${R_{surface} = {R_{core}{\sin( \frac{\pi}{N} )}}},$where N is said plurality of fibers.

In an embodiment, said first material has a refractive index in therange 1.5 to 2.2. In an embodiment, said first material has a refractiveindex in the range 1.85 to 2.05. Preferably, said first material has arefractive index of substantially 1.9.

In an embodiment, said first material is substantially opticallytransmissive at visible wavelengths of light. In an alternativeembodiment, said first material is substantially optically transmissiveat infra-red wavelengths of light and is substantially absorptive atvisible wavelengths of light.

In an embodiment, in step a. said core is formed having a circularcross-section. In an alternative embodiment, in step a. said core isformed having a non-circular cross-section, such as a square,rectangular or triangular cross-section.

“Retro-reflectivity” or “retro-reflection” refers to the opticalphenomenon in which reflected light rays preferentially follow a pathclose to the opposite of the direction from which they were incident ona medium.

“Textile” is typically (but need not be) a woven or knitted material,and can include a cloth and a fabric.

“Visible wavelengths” refers to wavelengths of light that lie within therange approximately 400 nm to 800 nm.

“Infrared” refers to the region of the electromagnetic spectrum thatlies at wavelengths longer than those associated with visible light(which range from approximately 400 nm to 800 nm) but at wavelengthsshorter than those associated with microwaves, which are typicallylonger than 1 mm.

The aspects noted above recite many features of the invention. Any ofthe features noted herein can be combined with any of the other featuresin any of the aspects, practices or embodiments of the inventiondescribed herein, except where clearly mutually exclusive or a statementis explicitly made herein that such a combination is unworkable orotherwise outside scope of the invention. To avoid undue repetition andlength of the disclosure, all the possible combinations of features arenot explicitly recited.

BRIEF SUMMARY OF DRAWINGS

FIG. 1 schematically illustrates a cross-section of a retro-reflectivethread according to a first embodiment of the invention;

FIG. 2 schematically illustrates a cross-section of a retro-reflectivethread according to a second embodiment of the invention;

FIG. 3 schematically illustrates retro-reflection of light from theretro-reflective thread of FIG. 2;

FIG. 4 schematically illustrates retro-reflection of light from aLambertian surface;

FIG. 5 schematically illustrates a cross-section of a retro-reflectivethread according to a third embodiment of the invention;

FIG. 6 schematically illustrates a cross-section of a retro-reflectivethread according to a fourth embodiment of the invention;

FIG. 7 shows a plot of retro-reflected power, RRR, as a function offiber refractive index for a retro-reflective thread according to afifth embodiment of the invention;

FIG. 8 shows a plot of retro-reflected power as a function of number offibers and fiber radius relative to internal section radius for aretro-reflective thread according to a sixth embodiment of theinvention;

FIGS. 9A-C schematically illustrate steps of a method of manufacturing aretro-reflective thread according to a seventh embodiment of theinvention;

FIG. 10 illustrates steps of a method of manufacturing aretro-reflective thread according to an eighth embodiment of theinvention;

FIG. 11 illustrates steps of a method of manufacturing aretro-reflective thread according to a ninth embodiment of theinvention;

FIG. 12 illustrates steps of a method of manufacturing aretro-reflective thread according to a tenth embodiment of theinvention;

FIG. 13 illustrates steps of a method of manufacturing aretro-reflective thread according to a twelfth embodiment of theinvention; and

FIG. 14 illustrates a textile according to a further embodiment of theinvention.

Not every component is labeled in every one of the foregoing figures,nor is every component of each embodiment of the invention shown whereillustration is not considered necessary to allow those of ordinaryskill in the art to understand the invention. The figures are schematicand not necessarily to scale.

When considered in conjunction with the foregoing figures, furtherfeatures of the invention will become apparent from the followingdetailed description of non-limiting embodiments of the invention.

DETAILED DESCRIPTION

Various features of the invention will be described with respect to thefollowing exemplary embodiments, however, the invention is not limitedto the following combinations of features. The various aspects of theinvention described herein can be combined and applied in the mannerneeded to further enhance, optimize or tune the optical performance toattain the results needed for a given application.

FIG. 1 illustrates an exemplary retro-reflective thread 100 comprisingan internal section 10, a plurality of fibers 12 and a reflectivematerial 14. Each fiber 12 comprises a respective longitudinal axis anda respective surface 12 a. Each fiber 12 comprises a first material thatis at least partially optically transmissive. The fibers 12 areconfigured with their respective longitudinal axes substantiallyco-linearly aligned with one another and the fibers 12 areinterconnected in series around the internal section 10. The fibers 12are just touching one another. A first part 12 b of the surface of eachfiber 12 faces into the internal section 10. The reflective material 14is provided on said first part 12 b of the surface of each fiber 12.

FIG. 2 illustrates a retro-reflective thread 200 according to a secondembodiment of the invention. In this embodiment the internal sectioncomprises a core fiber 20 having a longitudinal axis and a surface.There are twelve fibers 12 which are configured with their respectivelongitudinal axes substantially co-linearly aligned with thelongitudinal axis of the core fiber 20 and are arranged in series aroundthe surface of the core fiber 20. In this embodiment, the fibers 12 areslightly separated from one another.

The core fiber 20 is made of the reflective material, in this example ametal, such as Indium. The reflective material may alternatively be areflective alloy or a reflective particulate-doped material, such as atransparent polymer doped with particles of a reflective metal or alloy.The fibers 12 are made of a polymer that is transparent at visiblewavelengths of light, having a refractive index in the range 1.85 to2.05. The fibers 12 may for example be made of polypropylene orpolyester. The fibers 12 have a radius of 13 μm and the core fiber 20has a radius of 50 μm.

The retro-reflectivity of the retro-reflective thread 200 is attributedto the lensing action of the fibers 12 and the reflectivity of thereflective material of the core fiber 20. Referring to FIG. 3, incidentlight 24 a enters a fiber 12 and is refracted towards the opposite side.The incident light 24 a is then reflected at the interface of the fiber12 and the reflective core fiber 20. The outgoing light 24 b isretransmitted across the fiber 12 and exits the fiber 12.

Ray-tracing simulations have been performed to determine theretro-reflectivity of the retro-reflective thread 200. To ensureaccuracy of the simulations, comparison with measurements wereperformed. The measurement setup is illustrated in FIG. 4. Angle arefers to the angle of incidence or entrance angle, i.e. the anglebetween the incident light 24 a and the surface normal, x. Angle brefers to the observation angle, i.e. the angle between the incidentlight 24 a and the outgoing light 24 b. The light source was a weaklycollimated white light source with detector diodes directly adjacent toit. Thus direct retro-reflection could be measured. Retro-reflection ofa white light source from a Lambertian surface S was measured forcomparison.

Retro-reflection was measured for the following objects: 1) plain roundfibers, 2) the retro-reflective thread 200, and 3) a retro-reflectivebeads tape. For the retro-reflective thread, the fibers 12 were alignedin an array with enough space between them to prevent multiplescatterings.

First the retro-reflected power from the white Lambertian surface wasmeasured, then the retro-reflected power from the object was measured.The ratio between the two powers was then calculated. A ratio of greaterthan 100% indicates that the retro-reflective thread 200 exhibits moreretro-reflectivity than the Lambertian surface, while a ratio below 100%indicates less retro-reflectivity than the Lambertian surface.Measurements were made for entrance angles of 5°, 10°, 20°, and 30°. Theentrance angle is aligned orthogonal to the object. The observationangle was fixed at 0°. The following table lists the measuredretro-reflection of each object relative to the reference white Lambertian surface for each entrance angle:

Round polymer Retro-reflective Retro-reflective Entrance angle fiberthread bead tape  5° 22% 2583% 2539% 10° 22% 2542% 2539% 20° 23% 2708%2539% 30° 24% 2750% 2539%

FIG. 5 illustrates a retro-reflective thread 300 according to a thirdembodiment of the invention. In this embodiment the fibers 12 arearranged in a spaced series with a connecting element 30 providedbetween each pair of fibers 12, each connecting element 30interconnecting a respective pair of fibers 12.

FIG. 6 illustrates a retro-reflective thread 400 according to a thirdembodiment of the invention. In this embodiment the internal sectioncomprises a core fiber 40 having a longitudinal axis and a surface.There are eight fibers 12 which are configured with their respectivelongitudinal axes substantially co-linearly aligned with thelongitudinal axis of the core fiber 20 and are arranged in series aroundthe surface of the core fiber 20, interconnected by connecting elements30.

The core fiber 40 is made of the reflective material, in this example ametal. The reflective material may alternatively be a reflective alloyor a reflective particulate-doped material, such as a transparentpolymer doped with particles of a reflective metal or alloy. The fibers12 are made of a transparent polymer having a refractive index ofapproximately 1.9. The fibers 12 have a radius of 13 μm and the corefiber 20 has a radius of 50 μm.

The core fiber 40 may alternatively be made of a polymer material, thereflective material being provided as a coating layer between the fibers12 and the polymer core fiber 40.

The key parameter for achieving high retro-reflectivity in the thread400 is that the fiber-core fiber interface should be as lossless andreflective as possible, and fibers should have a refractive index ofclose to 1.9. This is illustrated in FIG. 7 which shows a plot 500 ofretro-reflection, RRR, as a function of the refractive index of thefibers 12 for a retro-reflective thread according to a fifth embodimentof the invention having twelve fibers 12, the fibers 12 each having aradius of 13 μm and the core fiber 20 having a radius of 50 μm. As canbe seen from the plot 500, to achieve the highest retro-reflection, thesurface fibers' refractive index must be between 1.85 and 2.05.

Packing as many fibers 12 around the core fiber 40 is also necessary toachieve the highest possible retro-reflection. The number of surfacefibers that can be fitted on the core fiber's surface without touchingis given by

$N = \frac{\pi}{\arcsin( \frac{R_{surface}}{R_{core}} )}$where R_(surface) is the radius of the fibers 12 and R_(core) is theradius of the core fiber 40. For particular combinations of the tworadii the number will be an integer, otherwise one can round down to theclosest integer. Given the number of fibers 12 and the core radius, onecan determine the radius of the fibers 12 that would just touch. Theoptimal number of fibers 12 for a given radius of the internal section,core fiber 40 in this embodiment, will cover as much as possible thecircumference of the internal section while not touching. Shown in theplot in FIG. 8 is the retro-reflected power as a function of both theradius of the fibers 12 normalized by the core fiber radius and thenumber of fibers 12 for a retro-reflective thread according to a sixthembodiment of the invention. The white line indicates the maximum radiusof the fibers 12 for a given number of fibers, i.e.,

${R_{surfce} = {R_{core}{\sin( \frac{\pi}{N} )}}}.$The optimal number of fibers 12 fora given radius is N, but N±1 willstill yield high performance. But, in general overlapping fibers aredetrimental to retro-reflection performance.

In the embodiments shown in FIG. 1 to FIG. 6 each of the fibers 12 has asubstantially circular cross-section. As an alternative embodiment, eachof the fibers 12 can be slightly non-circular, i.e. elliptical, incross-section. As illustrated in the table below, using fibers 12 havingan elliptical cross-section, with the semi-major axis along the corefiber 40 circumference (−10% deformation case) or along the radius ofthe core fiber 40 (+10% deformation case) cuts the retro-reflection inhalf, although it is still more than 10 times greater than for a whiteLambertian surface.

Fiber non-deformed −10% deformation +10% deformationRetro-reflection >2500% >1100% >1000% ratio

In the embodiments shown in FIG. 1 to FIG. 7 the internal section 10,20, 40 has a substantially circular cross-section. As an alternativeembodiment, the internal section 10, 20, 40 may have a non-circularcross-section, including, for example, a square cross-section, arectangular cross-section or a triangular cross-section.

In a further embodiment, the fibers 12 are made of a material that issubstantially optically transmissive at infra-red wavelengths of lightand is substantially absorptive at visible wavelengths of light.

FIG. 9 and FIG. 10 schematically illustrate the steps of an exemplarymethod 600 of manufacturing a retro-reflective thread. The method 600,700 comprises the steps of:

-   -   a. forming 70 a thread comprising a core 60 having an surface        and a plurality of fibers 12;    -   b. Removing 72 the core to form a void 62; and    -   c. delivering 74 a reflective material 64 in a fluid state into        the void.

In step a., each fiber 12 has a respective longitudinal axis and arespective surface. The fibers 12 are configured with their respectivelongitudinal axes substantially co-linearly aligned with one another. Ascan be seen in FIG. 9, the fibers 12 are interconnected in series aroundthe core 60. Each fiber 12 comprises a first material that is opticallytransmissive at visible wavelengths of light.

In step b., the core 60 is removed such that a first part 12 b of thesurface of each fiber 12 faces into the void 62. By delivering areflective material in a fluid state into the void 62, the reflectivematerial is provided on said first part 12 b of the surface of each ofthe fibers 12.

FIG. 11 illustrates the steps of a method 800 of manufacturing aretro-reflective thread according to a ninth embodiment of theinvention. In this embodiment, the fibers 12 are formed from atransparent polymer. The reflective material in a fluid state isdelivered 82 into the void 62, so that said first part 12 b of thesurface of each fiber 12 is coated with the fluid reflective material82. Fluid reflective material not coating a fiber 12 is then removed,leaving a coating of fluid reflective material on the fibers 12, and thereflective material is enabled to solidify to form a solid reflectivematerial coating on the fibers 12. A suitable reflective material in thefluid state would be a molten metal, such as molten Indium which may bepreferred due to its low absorption loss and its low melting point of157° C., which allows it to be deposited on the polymer fibers 12without damaging the fibers.

FIG. 12 illustrates the steps of a method 900 of manufacturing aretro-reflective thread according to a tenth embodiment of theinvention. In this embodiment, the void 62 is filled with reflectivematerial in a fluid state 92, for example, molten Indium, and thereflective material is enabled to solidify 94. A solid core fiber maytherefore be formed inside the fibers 12 formed in step a.

A further embodiment of the invention, described with reference to FIGS.9A-C, provides a method of manufacturing a retro-reflective thread inwhich step a. comprises extruding a bi-component polymer fiber havingthe cross-section shown in FIG. 9A). The outer fibers 12 are made of anon-water soluble polymer such as polypropylene. The core fiber 60 ismade of a water-soluble polymer. Around the outer rim of the core fiberand joining the fibers is a thin ring of the non-water soluble polymer,forming connecting elements 30. In step b., FIG. 9B, the bi-componentpolymer fiber is exposed to water in order to dissolve the water-solublecore fiber 60, forming a void 62 internally to the fibers 12 and theconnecting elements 30. In step c., FIG. 9C, molten metal is pumped intothe void 62. Then either, the inside surface is coated, extraneousmolten metal is removed and the molten metal allowed to solidify to forma metal coating, or the void 62 is filled and the molten metal isallowed to solidify to form a solid metal core fiber 64.

FIG. 13 illustrates the steps of a method 900 of manufacturing aretro-reflective thread according to a twelfth embodiment of theinvention. In this embodiment, which is similar to the method 800 ofFIG. 11, following formation of a solid reflective coating on the insideof the fibers 82, 84, the remaining void is filled with a polymer in afluid state and the polymer is enabled to solidify, to thereby form asolid polymer core fiber.

FIG. 14 illustrates a textile 1100 comprising at least oneretro-reflective thread 100 as illustrated in FIG. 1. It will beappreciated by one of ordinary skill in the art that any of theretro-reflective threads 200, 300, 400 illustrated with reference toFIGS. 2 to 8 may alternatively be incorporated into a textile.

In a further embodiment, a textile is provided which is woven from aplurality of retro-reflective threads 100 as illustrated in FIG. 1. Itwill be appreciated by one of ordinary skill in the art that any of theretro-reflective threads 200, 300, 400 illustrated with reference toFIGS. 2 to 8 may alternatively be woven into a textile.

Textiles with retro-reflective threads incorporated into patterns ofwoven, braided, knitted and spun, and the like patterns, may have uniqueoptical properties as a result of the continuously curved surface andresulting continuously varying angle of incidence of light.

The present disclosure is directed to each individual feature, system,material, and/or method described herein. In addition, any combinationof two or more such features, systems, materials, and/or methods, ifsuch features, systems, materials, and/or methods are not mutuallyinconsistent, is included within the scope of the present invention. Toavoid undue repetition, not all features are discussed in conjunctionwith every aspect, embodiment or practice of the disclosure. Featuresdescribed in conjunction with one aspect, embodiment or practice aredeemed to be includable with others absent mutual inconsistency or aclear teaching to the contrary. In some instances, features will bediscussed generally rather than in detail in conjunction with a specificaspect, embodiment or practice, and it is understood that such featurescan be included in any aspect, embodiment or practice, again absentmutual inconsistency or a clear teaching to the contrary.

Those of ordinary skill in the art will readily envision a variety ofother means and structures for performing the functions and/or obtainingthe results or advantages described herein and each of such variationsor modifications is deemed to be within the scope of the presentinvention. More generally, those skilled in the art would readilyappreciate that all parameters, dimensions, materials and configurationsdescribed herein are meant to be exemplary and that actual parameters,dimensions, materials and configurations will depend on specificapplications for which the teachings of the present invention are used.Accordingly, the foregoing embodiments are presented by way of exampleonly and that within the scope of the appended claims, and equivalentsthereto, the invention may be practiced otherwise than as specificallydescribed.

In the claims as well as in the specification above all transitionalphrases such as “comprising”, “including”, “carrying”, “having”,“containing”, “involving” and the like are understood to be open-ended.Only the transitional phrases “consisting of” and “consistingessentially of” shall be closed or semi-closed transitional phrases,respectively, as set forth in the U.S. Patent Office Manual of PatentExamining Procedure § 2111.03, 8th Edition, Revision 8. Furthermore,statements in the specification, such as, for example, definitions, areunderstood to be open ended unless otherwise explicitly limited.

The phrase “A or B” as in “one of A or B” is generally meant to expressthe inclusive “or” function, meaning that all three of the possibilitiesof A, B or both A and B are included, unless the context clearlyindicates that the exclusive “or” is appropriate (i.e., A and B aremutually exclusive and cannot be present at the same time). “At leastone of A, B or C” (as well as “at least one of A, B and C”) reads on anycombination of one or more of A, B and C, including, for example thefollowing: A; B; C; A & B; A & C; B St C; as well as on A, B & C.

It is generally well accepted in patent law that “a” means “at leastone” or “one or more.” Nevertheless, there are occasionally holdings tothe contrary. For clarity, as used herein “a” and the like mean “atleast one” or “one or more.” The phrase “at least one” may at times beexplicitly used to emphasize this point. Use of the phrase “at leastone” in one claim recitation is not to be taken to mean that the absenceof such a term in another recitation (e.g., simply using “a”) is somehowmore limiting. Furthermore, later reference to the term “at least one”as in “said at least one” should not be taken to introduce additionallimitations absent express recitation of such limitations. For example,recitation that an apparatus includes “at least one” feature with aparticular characteristic does not mean the claim requires all featuresto have the specified characteristic.

What is claimed is:
 1. A retro-reflective thread comprising: an internalsection; a plurality of fibers, each said fiber comprising a respectivelongitudinal axis and a respective surface and each said fibercomprising a first material that is at least partially opticallytransmissive, and wherein said plurality of fibers are configured withtheir respective longitudinal axes substantially co-linearly alignedwith one another and said plurality of fibers are interconnected inseries around said internal section and wherein a first part of saidrespective surface of each of said plurality of fibers faces into saidinternal section; and a reflective material provided on said first partof said respective surface of each of said plurality of fibers.
 2. Theretro-reflective thread of claim 1, wherein each of said plurality offibers is one of substantially circular in cross-section andsubstantially elliptical in cross-section.
 3. The retro-reflectivethread of claim 1, wherein said internal section is substantiallycircular in cross section and has radius, R_(core), and each said fiberhas a radius, R_(surface), and wherein said plurality of fibers, N, isinversely proportional to the ratio of R_(surface) to R_(core).
 4. Theretro-reflective thread of claim 1, wherein said internal section issubstantially circular in cross section and has radius, R_(core), andeach said fiber has a radius, R_(surface), and wherein each of saidplurality of fibers is arranged just touching a directly preceding oneof said plurality of fibers and just touching a directly subsequent oneof said plurality of fibers, and said plurality of fibers, N, is givenby${N = \frac{\pi}{\arcsin( \frac{R_{surface}}{R_{core}} )}}.$5. The retro-reflective thread of claim 1, wherein said the maximumradius, R_(surface), of each of said plurality of fibers is given by${R_{surface} = {R_{core}{\sin( \frac{\pi}{N} )}}},$ where Nis said plurality of fibers.
 6. The retro-reflective thread of claim 1,wherein interconnected in series comprises said plurality of fibersarranged in a spaced series and the retro-reflective thread furthercomprises a plurality of connecting elements, each of said plurality ofconnecting elements being located between and interconnecting arespective pair of said plurality of fibers.
 7. The retro-reflectivethread of claim 1, wherein interconnected in series comprises each ofsaid plurality of fibers arranged touching a directly preceding one ofsaid plurality of fibers and touching a directly subsequent one of saidplurality of fibers.
 8. The retro-reflective thread of claim 1, whereinsaid first material is one of a substantially transparent polymer and aglass.
 9. The retro-reflective thread of claim 1, wherein said firstmaterial has a refractive index in the range 1.5 to 2.2.
 10. Theretro-reflective thread of claim 1, wherein said first material has arefractive index in the range 1.85 to 2.05.
 11. The retro-reflectivethread of claim 1, wherein said first material has a refractive index ofsubstantially 1.9.
 12. The retro-reflective thread of claim 1, whereinsaid first material is substantially optically transmissive at visiblewavelengths of light.
 13. The retro-reflective thread of claim 1,wherein said first material is substantially optically transmissive atinfra-red wavelengths of light and is substantially absorptive atvisible wavelengths of light.
 14. The retro-reflective thread of claim1, wherein said reflective material is one of a reflective metal, areflective alloy and a polymer doped with reflective particles.
 15. Theretro-reflective thread of claim 1, wherein said reflective materialcomprises a coating provided on said first part of said respectivesurface of each of said plurality of fibers.
 16. The retro-reflectivethread of claim 1, wherein said internal section comprises a polymercore.
 17. The retro-reflective thread of claim 1, wherein said internalsection comprises a core of said reflective material.
 18. Theretro-reflective thread of claim 1, wherein said internal section hasone of a circular cross-section and a non-circular cross-section.
 19. Atextile comprising at least one retro-reflective thread comprising: aninternal section; a plurality of fibers, each said fiber comprising alongitudinal axis and a surface and each said fiber comprising a firstmaterial that is at least partially optically transmissive, and whereinsaid plurality of fibers are configured with their respectivelongitudinal axes substantially co-linearly aligned with one another andsaid plurality of fibers are interconnected in series around saidinternal section and wherein a first part of said surface of each ofsaid plurality of fibers faces into said internal section; and areflective material provided on said first part of said surface of eachof said plurality of fibers.